Field of the Invention
This present disclosure relates to extended interaction devices (EIDs), and more particularly to a millimeter-wave EID comprising coaxial resonant cavities and multiple electron beams.
Description of background art
The output power of millimeter-wave sources based on vacuum electronic technology is mainly limited by two aspects: 1 ) The structure size of devices operated in a fundamental mode is becoming ever smaller with increasing operating frequency, which limits the improvement of the available electron beam current in millimeter-wave devices and lowers output power. 2 ) Operating the device in a fundamental mode at high frequency requires reducing the size of the resonant cavity (the size of the resonant cavity is inversely proportional to the frequency). This inevitably increases the processing difficulty and production cost of the device.
Adopting a larger size device should allow for a high-order mode. However, a high-order mode operation would suffer from mode competition and coupling impedance limits, dramatically lowering the operation stability and efficiency of the device or even causing the device to fail.
There are three main methods used to improve output power of millimeter-wave sources based on vacuum electronic technology. The first one is to adopt multiple electron beams to reduce the operating voltage of the device. The transverse space for placing multiple beams is limited because the interaction structure is a traditional reentrant resonant cavity, which restricts the maximum number of available multiple beams or the total area in the transverse direction of all beams. The second method exploits sheet electron beam. The total operating current can be increased to improve output power by distributing sheet beam in a transverse direction. However, the enlargement of the transverse space is limited and extending further the space would introduce mode competition. As the third method, a ring strip electron beam can be employed to obtain higher output power by increasing electron emission area and electron beam tunnel area. There are practical limits to this method because a high-quality ring strip electron beam is difficult to achieve.